Abstract

4184

RNA interference (RNAi) offers unique opportunities to become a novel therapeutic modality in combating cancer. Although highly target specific its use has been limited by its short duration of therapeutic gene expression. To overcome this shortcoming, we constructed an oncolytic adenovirus (Ad)-based shRNA expression system (Ad-ΔB7-shVEGF) against vascular endothelial growth factor (VEGF), a key mediator in angiogenesis. To demonstrate VEGF-specific nature of this newly engineered Ad-based shRNA, replication-incompetent Ad expressing VEGF-specific shRNA (Ad-ΔE1-shVEGF) was also generated. Ad-ΔE1-shVEGF was highly effective in reducing VEGF expression, and elicited anti-angiogenenic effect in vitro as well as in vivo. Similarly, Ad-ΔB7-shVEGF exhibited potent anti-angiogenic effects in the matrigel plug assay in vivo. Moreover, Ad-ΔB7-shVEGF also demonstrated enhanced antitumor effect and survival advantage compared to its cognate control oncolytic Ad, Ad-ΔB7. Tumor histological analysis revealed that Ad-ΔB7-shVEGF induced significant reduction in tumor vasculature, verifying the anti-angiogenic mechanism. Furthermore, the duration and magnitude of the gene silencing effect following infection with Ad-ΔB7-shVEGF was longer and more effective than the replication-incompetent Ad, Ad-ΔE1-shVEGF. Taken together, these results suggest that the combined effects of oncolytic viral therapy and cancer cell-specific expression of VEGF-targeted shRNA elicits greater anti-tumor effect than an oncolytic Ad alone.